Osteoarthritis (OA) is the most prevalent joint disease. Therapies for established and measures to prevent OA are not available. While aging is a major OA risk factor, mechanisms of joint and cartilage aging remain to be characterized. Our overall hypothesis proposes that cartilage aging is associated with failure of cellular homeostasis mechanisms, causing cell dysfunction and death. This initially affects the superficial zone and triggers the cartilage remodeling and degradation process characteristic of OA. The overall goal of this program is to begin with phenotype identification, proceed to elucidation of mechanisms and key cellular and molecular abnormalities in order to provide new directions for correction of aging-associated risk factors for OA and therapeutic interventions for established OA. In this proposal we focus on the identification of early changes in cellular and joint homeostasis mechanisms upon which OA is triggered or accelerated in response to biomechanical or biochemical stressors. This competing renewal continues to utilize human knee joints from donors across the adult age spectrum to establish phenotypic changes in articular cartilage and other joint tissues that are characteristic of normal joint aging and may predispose to OA development. Access to human tissues provides a unique opportunity to test the human and clinical relevance of novel basic and molecular mechanisms not only through correlative studies but also through an array of mechanistic studies with cells isolated from human tissues. These studies will be complemented with mutant mouse models. The proposed program will continue the existing cores (A: Administration; PI M. Lotz; B: Tissue Acquisition, Morphology, and Cell Culture; PI D. D'Lima). The following 3 projects are proposed: Project 1 'Autophagy in Aging and Osteoarthritis' (PI M. Lotz) will characterize patterns and consequences of defective and pharmacologically enhanced autophagy in joint aging and OA; Project 2 'The Chondrocyte Unfolded Protein Response (UPR) in Aging and Osteoarthritis' (PI R. Terkeltaub) addresses mechanisms and consequences of impaired UPR in regards to chondrocyte survival and hypertrophy; and Project 3 'Mechanobiology of Human Articular Cartilage Degeneration: Aging and Osteoarthritis' (PI R. Sah) will analyze biomechanical mechanisms of early and advanced cartilage degeneration and determine consequences for chondrocyte function and survival.